Zwicky [168]
noted a deficiency of clusters behind the Coma cluster
as compared to other regions of the sky. He interpreted this deficiency
as evidence
for IC extinction, presumably due to diffuse dust. Later, Noonan
[101]
found evidence for IC extinction of ~ 0.4 mag in the blue band, in
agreement with the estimate given by Karachentsev & Lipovetskii
[77].
Few years later, Wesson
[151]
made the rather extreme
hypothesis that IC dust may be present in such large quantities as to bind the
Coma cluster!

The IC dust hypothesis encountered more criticism than consensus.
In the 60's de Vaucouleurs noted that the fact that diffuse
gas remained undetected implied a low density of diffuse dust, and
Abell [4]
considered the evidence for IC inconclusive.
Smart [125]
showed that IC dust must be significantly depleted because of
the dust grain sputtering by the hot IC gas.
Tifft & Gregory
[138]
identified a group in the background of Coma and
showed that the magnitudes of galaxies in this group
are not significantly affected by extinction.

Recently, Dwek et al.
[41]
modelled the formation and evolution of IC dust
in Coma, including sputtering from the IC gas and dust injection from galaxies.
They derived a dust density much below that required to explain the observed
visual extinction, but consistent with the upper limit reported by
IRAS for IR emission in the Coma region. Ferguson
[46], using
the Mg2-(B-V) relation for Coma ellipticals, set an upper limit
of E(B-V) ~ 0.05 for IC extinction.

The amount of IC dust recently detected with ISO
(Stickel, these proceedings) is even lower than what predicted by Dwek et
al.'s model.